International air travel to and from the U.S. has more than doubled in the last 20 years according to a new report from the Brookings Institution. In 2011, passengers made 152 million trips, with a majority of international passengers traveling through major metropolitan gateways such as New York, San Francisco, Charlotte, and Seattle.

Adie Tomer, a senior research associate atBrookings, says the report may cause the government to reconsider its allocation of airport funding. "Over 90 percent of domestic and international passengers in the United States travel through the 100 largest metropolitan areas," says Tomer, yet "the major federal capital grant program sends only 36 percent of funding to those particular airports."